When an organic EL display apparatus is manufactured, for example, an organic layer is deposited at places corresponding to respective pixels on an apparatus substrate wherein switching elements such as TFTs are formed on a support substrate. Therefore, a deposition mask is placed on the apparatus substrate beforehand and thereafter an organic material is disposed on the substrate via the deposition mask, resulting that a required amount of organic layer can be deposited for only required pixels. A metal mask has been conventionally used as the deposition mask. However, in order to form much fine pattern of mask openings, a recent trend is that resin films are used as mask material instead of the metal masks.
On the other hand, the deposition mask causes an organic material sublimated from a vapor deposition source to adhere to a substrate for vapor deposition via its opening, a crucible of the vapor deposition source used for vapor deposition in this case is heated up to a high temperature to cause the organic material, being a vapor deposition material, to sublimate. Therefore, the temperature of the deposition mask is increased by heat radiated from the vapor deposition source, the deposition mask material expands thermally, and the deposition mask deforms. Such deformation of the deposition mask induces position gap of an opening pattern of the deposition mask, imparts an adverse influence on positional accuracy and opening size, and deteriorates display quality when an organic EL display apparatus is formed.
In order to prevent position gap caused by such thermal deformation, for example, in a conventional metal mask, it is disclosed that invar or the like, which has a smaller coefficient of thermal expansion and hardly expands when heated, is used as a mask material (Patent Document 1). In addition, it is disclosed that a thermal barrier material is provided between a deposition mask and a vapor deposition source to absorb heat radiated from a vapor deposition source and release heat to the outside, thereby suppressing the temperature rise of the deposition mask (Patent Document 2).
Furthermore, when a resin film is used as a mask material, the coefficient of thermal expansion of any film is relatively greater compared with invar and it is difficult to solve the problem by material selection. In addition, when the vapor deposition source moves during layer formation like a linear source, since the temperature distribution in the mask varies with the movement of the vapor deposition source and the opening position displaces correspondingly, the size of a vapor deposited layer becomes greater than the opening size of the deposition mask.